Braun Group People
Corissa Lee
Graduate Student in Materials Science and Engineering
B.S. in Materials Science and Engineering from Cornell University (2008)
Damage and ultimate failure of polymeric materials result from stress-induced, unselective covalent bond scission. A relatively unexplored alternative to this mechanochemical degradation process is the productive channeling of mechanical energy to activate chemical pathways that favorably alter or enhance the material properties of the polymer, analogous to the responsive behavior of biological systems.
Mechanochemical molecular probes have been developed in the Autonomous Materials Systems group (AMS) here at the University of Illinois, with damage assessment capabilities at the single-molecule detection limit. Mechanically induced covalent bond changes enable new strategies for post-processing modifications of polymeric materials that impart self-sensing and potentially self-reinforcing capabilities. Molecular force sensor or mechanophores, are the force-activated building blocks of mechanoresponsive materials. These materials undergo productive chemical changes prior to polymer chain scission. Members in the AMS group have already demonstrated that commonly encountered mechanical forces can be translated into selective covalent bond breakage in solid polymers, triggering a localized mechanochemical reaction. The mechanophore spiropyran was linked into elastomeric and glassy polymer solids. Mechanical stress was applied to the bulk polymer sample, causing rupture of the spiro carbon-oxygen (C-O) bond turning the closed, colorless spiropyran molecule into the planar merocyanine (MC) molecular conformation (Figure 1). This biased reaction resulted in immediate color change and fluorescence of the bulk polymer (Figure 2).
Figure 1
Figure 2
My research involves further studying the mechanophore spiropyran as a molecular force sensor in other polymer systems which may facilitate mechanophore attachment at an interface. Goals involve demonstrating mechanochemistry at an interface between some type of reinforcement phase and a matrix phase, similar to that of a composite. Other goals involve studying the opening and closing kinetics of the spiropyran to merocyanine in polymer matrixes using fluorescence and absorption techniques. Information gained from these studies may help in quantifying the energies and forces required for activation of this mechanophore.
• Davis, D.A., Hamilton, A., Yang, J., Cremar, L.D., van Gough, D., Potisek, S.L., Ong, M.T., Braun, P.V., Martínez, T.J., Moore, J.S., White, S.R., Sottos, N.R., “Mechanochemical Transduction in Polymeric Materials,” accepted, Nature (2009).
• Hickenboth, C.R., Moore, J.S., White, S.R., Sottos, N.R., Baudry, J., Wilson, S.R., ''Biasing reaction pathways with mechanical force" Nature, 446, 423-427 (2007).
Professor Paul Braun • Phone: +1.217.244.7293 • Fax: +1.217.333.2736 • Email: pbraun@illinois.edu
Department of Materials Science and Engineering • University of Illinois at Urbana-Champaign